Semiconductor devices, such as transistors, microprocessors, etc., have been designed and fabricated in ever smaller and smaller sizes. However, such miniaturization has in recent years encountered a fundamental size limitation. As devices are constructed with dimensions of less than about 1/4 of a micron, "troublesome" quantum wave effects begin to dominate the characteristics of the device. For example, electron charge flow in nanometer-size wires is greatly affected by a bend in the wire. Another example of these observed effects is electron wave "self-interference".
Semiconductor growth and fabrication techniques, such as molecular beam epitaxy, metalorganic chemical vapor deposition, and nanolithography, have been refined to the point that semiconductor structures can be fabricated with device dimensions on the order of electron wavelengths. Using these techniques, devices exhibiting ballistic (i.e., collisionless) electron transport have been fabricated. Starting from fundamental principles, it has been shown that these ballistic electrons are quantum-mechanical deBroglie waves and can be reflected, refracted, diffracted, guided, and interfered in a manner analogous to plane waves in dielectric materials. This has led to a new class of ultra-small, ultra-fast devices such as those shown in U.S. Pat. Nos. 4,985,737 of Gaylord, et al., 4,987,458 of Gaylord, et al., and 4,970,563 of Gaylord, et al.
Technical papers published in 1988 and 1989 discuss a ballistic electron transistor device based on diffraction of an electron wave from a 50% duty-cycle potential energy grating formed by a superlattice. See, K. Furuya, "Novel High-Speed Transistor Using Electron Wave Diffraction," J. Appl. Phys., Vol. 62, pp. 1492-1494, Apr. 21, 1989; K. Furuya and K. Kurishima, "Theoretical Properties of Electron Wave Diffraction Due to a Transversally Periodic Structure in Semiconductors," IEEE J. Quantum Elect., Vol. 24, pp. 1652-1658, August 1988; and K. Kurishima, K. Furuya and S. Samadi, "Theoretical Study of Electron Wave Diffraction Caused by Transverse Potential Grating----Effect of Incident Angle," IEEE J. Quantum Elect., Vol. 25, pp. 2350-2356, November 1989. The analysis presented in these papers is limited to the 50% duty-cycle with no variation in effective mass. Also, these papers do not present an approach that can be employed to construct a grating profile which would be designed to produce an arbitrary desired result. Importantly, the device discussed in these papers diffracts the input electron beam into a large number (not preselected) of output beams, making the device impractical as a switch or multiplexor. Furthermore, these papers and the existing state of the art known to the applicants do not disclose a quantum mechanical electron/hole device in the form of a switch or multiplexor.
Accordingly, it can be seen that a need yet remains for quantum mechanical semiconductor devices with electron/hole diffractive gratings which can be useful as switches, multiplexors, etc. It is for the provision of such that the present invention is primarily directed.